Rebirth, on the 21st of Vult, is the new year for followers of the Silver Flame. It takes place on the date of the winter solstice, representing the end of the long nights and a return to the light and warmth of the dawn. The faithful spend the whole night holding vigil and guarding against evil. The next day is spent resting or celebrating, depending on the individual.
Source: Sarhain's Guide to the Silver Flame
The Purified new year, Rebirth Eve occurs on the winter solstice. It celebrates the passing of the longest night, when the world begins its slow journey toward light and warmth. The faithful stay up the entire night, holding spiritual vigil and guarding against evil, and spend the following day in rest or celebration, as they see fit.
Source: Faiths of Eberron